Adhesives for making multilayer films comprising liquid crystalline polymer and polypropylene

ABSTRACT

Multilayer films that include a thermotropic liquid crystalline polymer film layer and a polypropyene film layer are bound together using hot melt adhesives which may be either (1) a blend of poly( alpha -olefins), comprised of isotactic polypropylene, a polymer of a second lower poly( alpha -olefin), and a small amount of a higher poly( alpha -olefin), or (2) a blend of poly(propylene-graft-maleic anhydride) and a dimer acid based polyamide. These hot melt adhesives also act as compatiblizers for blends of polypropylene and thermotropic liquid crystalline polymers.

RELATED APPLICATIONS

The following four copending applications filed on even date herewith,all contain related subject matter: U.S. application Ser. Nos.08/954,377, 08/954,379, 08/954,997 and 08/955,000.

FIELD OF THE INVENTION

This invention relates to multilayer films, and more specifically tomultilayer films that include a liquid crystalline polymer film and apolypropylene film.

BACKGROUND OF THE INVENTION

Liquid crystalline polymer (LCP) films have properties that are verydesirable, such as excellent chemical resistance, high strength, andexcellent gas barrier properties. However, these same films have certainundesirable properties. They often have poor transverse mechanicalproperties (i.e. they are strong in the machine direction, but teareasily in the direction transverse to the machine direction). It is alsodifficult to write or print on the films. LCP films are more expensivethan conventional polymer films, such as polyester films.

It would be desirable to make multilayer films having LCP film bonded toone or more other films to obtain a film having the best properties ofall of the various layers, such as a multilayer film having the good gasbarrier properties of an LCP and the relatively low cost of aconventional polymer.

However, LCP films do not bond well to each other or to other films byuse of an adhesive. Their surfaces do not in general adhere toadhesives. There are thus very few examples of multilayer filmscontaining one or more LCP layers. Multilayer films in which LCP's andpolypropylene are bound together are also rarely mentioned. One examplecan be found in Japanese Patent Application No. 02-253,950, published in1990, where a poly(butylene terephthalate) film layer is bound toVECTRA® A 900 LCP film using a glycidyl-modified ethylene vinyl acetateadhesive. The other side of the VECTRA film is bound to polypropylenefilm by using two adhesive layers, a glycidyl-modified ethylene vinylacetate layer in contact with the LCP and an ethylacrylate-ethylene-maleic anhydride copolymer in contact with thepolypropylene. Japanese Patent publications 02-253,951 (1990) and04-135,750 (1992) use similar adhesives for binding an LCP topoly(butylene terephthalate) and polypropylene. The latter of thesepatent applications also uses a saponified ethylene-vinyl acetatecopolymer as an adhesive. Other publications that discuss multilayerfilms comprising an LCP barrier layer include Japanese PatentPublication 02-307,751 (1990), PCT Patent Publication WO 95/23180, andEuropean Patent Application No. 763,423.

SUMMARY OF THE INVENTION

Adhesives have now been identified that bind LCP films having severaldifferent compositions to polypropylene. These adhesives are all hotmelt adhesives and are summarized as follows:

(1) A polyolefin blend, which is a mixture of poly(α-olefins), comprisedmainly of isotactic polypropylene and a polymer of a second lowerα-olefin, with small amounts of higher poly(α-olefins).

(2) A blend of two hot melt adhesives: (1) Poly(propylene-graft-maleicanhydride) and (2) dimer acid based polyamide. These work well in blendshaving each polymer included in an amount of 30-70% by weight, with a50:50 blend by weight being particularly satisfactory.

Multilayer films are made by heating the two films that are being bondedtogether to a temperature above the melting points of both polymers andof the hot melt adhesive, under a compressive force, to form laminatedstructures, or by coextruding the molten polymers, including adhesives,through a die slit to form multilayer films.

The adhesives described above also turn out to be compatibilizers forblends of the LCP and polypropylene. The blends are made by extrudingthe LCP, the other polymer, and the adhesive/compatibilizer in themolten phase through an extruder under mixing conditions.

The words "films" and "sheets" and "films and sheets" are all usedherein to describe thin flexible plastic fabricated structures. Thesegenerally have a thickness in the range of about 0.01 mm (0.4 mils) toabout 10 mm (400 mils). This range of thicknesses is wide enough toencompass the common meaning of both films (<0.25 mm) and sheets(thicker than films), and the words "films" and "sheets" therefore areused interchangeably to describe something that may be described eitheras a film or sheet. The layers in coextruded films and sheets willlikewise have the same broad range of thicknesses described above (i.e.about 0.01 mm to about 10 mm). The laminated and coextruded structureswill be thicker since they are made up of several layers or films.Finally, "multilayer" sheets and films includes both laminated sheetsand films and coextruded sheets and films. Laminated sheets and filmsare made by laminating sheets and films together. Coextruded sheets andfilms are made by coextruding the polymers through the die of anextruder in such a way that a multilayer film or sheet is formed.Multilayer films are also sometimes referred to as "laminates,"regardless of how they are made.

DETAILED DESCRIPTION OF THE INVENTION

Liquid crystalline polymers (LCP's) are well known in the art and arecharacterized as having a liquid crystalline phase above the temperatureat which the polymers become molten. The liquid crystalline polymersused in the multilayer films described herein are generally all-aromaticpolymers, with relatively linear structures, which exhibit liquidcrystalline behavior in the molten phase. They are generally polyestersor poly(ester-amides), and generally comprise monomer units that includewithin their structures, exclusive of functional groups, one or more ofthe following aromatic nuclei: 1,4-phenylene, 1,3-phenylene,4,4'-biphenylene, and 2,6- and/or 2,7-naphthalene. Some LCP's alsocontain monomer units that are derived from ethylene glycol. PreferredLCP's contain only aromatic monomer units.

Generally, the LCP's comprise monomer units derived from one or more ofthe following monomers and generally at least two of the followingmonomers: terephthalic acid, isophthalic acid, 1,4-hydroquinone,resorcinol, 4-aminobenzoic acid, 4-hydroxybenzoic acid, 4-aminophenol,1,4-phenylenediamine, 4,4'-biphenol, 4,4'-biphenyldicarboxylic acid,6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid, and2,6-dihydroxynaphthalene. Preferred LCP's include the polymers that aresold under the VECTRA® trademark, most of which comprise monomer unitsderived from 6-hydroxy-2-naphthoic acid (HNA) and 4-hydroxybenzoic acid(HBA) in their structure. Particularly preferred polymers from theVECTRA products are the VECTRA A polymers, made up of about 73% HBAmonomer units and 27% HNA monomer units, and VECTRA E products, whichcontain HBA, HNA, 4,4'-biphenol (BP) and terephthalic acid (TA) asdescribed in U.S. Pat. No. 4,473,682, incorporated herein by reference.The polyesteramide comprising HBA, HNA, BP, TA and 4-aminophenol, taughtin U.S. Pat. No. 5,204,443, which is also incorporated herein byreference, is also useful with these adhesives. All of these productsare available from Hoechst Technical Polymers, Summit, New Jersey.Another LCP which may be used in multilayer films using the adhesivestaught herein is disclosed in U.S. Pat. No. 5,656,714, incorporatedherein by reference, and comprises monomer units derived from HBA, HNA,BP, TA, and resorcinol. LCP's comprising BP, HBA, TA, and other optionalmonomers are available from Amoco Chemicals under the XYDAR® trademark.LCP's containing 2,6-naphthalenedicarboxylic acid, BP, and other monomerunits are also available from DuPont. Films made from all of thesepolymers can be made into multilayer films using the adhesives andmethods taught herein.

The following LCP's were tested herein for the purpose of obtainingmultilayer films:

(1) VECTRA® A film, comprised of monomer units derived from HBA and HNAin a ratio of about 73:27, and having a melting temperature of about280° C.

(2) VECTRA® B Resin, which is a polyesteramide comprising monomer unitsderived from HNA, TA, and 4-aminophenol (see U.S. Pat. No. 4,330,457)and which has a melting temperature of about 280° C.

(3) VECTRA® L Resin, which is a liquid crystalline poly(esteramide)comprised of monomer units derived from HBA, HNA, BP, TA and4-aminophenol in accordance with U.S. Pat. No. 5,204,443. This resin hasa melting temperature of 302° C.

(4) An experimental LCP polyester, comprising monomer units derived fromHBA, HNA, HO, and TA, referred to hereinafter as Experimental Polymer 1.It has a melting temperature of about 220° C.

(5) An experimental LCP polyester film that has been modified to havebetter adhesion by including monomer units that have sulfonate groups.It comprises monomer units made from about 73 mole % HBA, about 27 mole% HNA, and the sodium salt of 5-sulfoisophthalic acid (0.2 mole %). Ithas a melting point of 270° C., and is further described in U.S. Pat.No. 5,227,456 which is incorporated herein by reference. It is referredto hereafter as Experimental Polymer 2.

(6) An experimental liquid crystalline polymer that comprises monomerunits derived from HBA, HNA, BP, TA, and resorcinol, as described inU.S. Pat. No. 5,656,714. It is referred to hereafter as ExperimentalPolymer 3.

Some of the polymers, e.g. VECTRA® A, B, and L resins are availablecommercially as glass-filled polymer resins or as films. VECTRA® A resinis available as fiber, film, or filled resin.

The polypropylene to which the LCP films are bound by using theadhesives disclosed herein is a commercially available resin that iswidely used in various fabricated products, including sheets and films.The sheets and films can be purchased as sheets and films or made frompolypropylene resin.

The types of adhesives that are useful in this invention are allcommercially available and are described in more detail below.

Polyolefin Blend

MACROMELT® Q5353 hot melt adhesive from Henkel Corporation turned out tobe an excellent hot-melt adhesive for combining LCP films withpolyethylene, polypropylene, polycarbonate, poly(ethyleneterephthalate), and poly(phenylene sulfide). The material appears to bea mixture of poly(α-olefins), consisting mainly of isotacticpolypropylene and a polymer of a second lower α-olefin, perhaps atacticpoly(1-butene), combined with a small amount of one or more higherpoly(α-olefin) oligomers. The material exhibits a trace of carbonylabsorption under infrared analysis, and traces of aromatic absorptionsby C¹³ -NMR analysis, but both are at levels of <3 mole %. The materialis described in U.S. Pat. No. 5,512,625, which is incorporated herein byreference. The patent indicates that the polyolefin blend comprises anoligomer of an α-olefin with at least 8 carbon atoms in the monomerblended with a substantially amorphous poly(α-olefin) (perhaps atacticpoly(1-butene)) and a substantially crystalline poly(α-olefin) (e.g.isotactic polyproylene).

Blend of Poly(propylene-graft-maleic anhydride) and Dimer Acid BasedPolyamide

A blend of the poly(propylene-graft-maleic anhydride) and dimer acidbased polyamide makes a good adhesive for binding LCP films topolypropylene films, whereas neither of the adhesive components alone issuitable. These are blended in a ratio of about 30:70 to about 70:30 byweight, with 50:50 blends (by weight) being particularly suitable. Thepoly(propylene-graft-maleic anhydride) is essentially polypropylene withmaleic anhydride units grafted onto the polymer chain. A satisfactoryproduct is sold under the trademark POLYBOND® 3002 polymer modifier, andis manufactured by Uniroyal Chemical. The material has a density of 0.91g/cc at 23° C. (ASTM D-792), a melting point of 157° C. by DSC, and amelt flow rate of 7.0 g/10 min, measured at 230° C. under a 2.16 kgweight in accordance with ASTM D-1328. It is sold as a compatibilizerfor blends of polypropylene with polyamide or ethylene-vinyl alcohol oras a chemical coupling agent for inorganic fillers in polypropylene. Itis desirable that if alternative poly(propylene-graft-maleic anhydride)polymers are used, that they have a melt flow index rate of at leastabout 4.0 g/10 min under the conditions above and a melting temperatureof at least 130° C.

The other component of the blend is a polyamide based on dimer acid,where dimer acid is a mixture of dimers of C₁₈ unsaturated fatty acids.The 36-carbon dimers are then polymerized with diamines to yieldpolyamides that are useful as hot melt adhesives. A dimer acid basedpolyamide that works well in this application is MACROMELT® 6239,supplied by Henkel Corporation. The material has a softening point (Balland Ring) of 133°-143° C., a melt viscosity of 55-85 poise at 225° C.,and an application temperature of 249°-265° C. It is sold as an adhesivefor ABS polymers and flexible vinyl polymers. Other hot melt polyamidesshould be suitable provided they have an application temperature nearthe melt temperature of the polymers in the blend and suitableviscosities.

Methods of Making Laminated Films and Sheets

The films and sheets are most conveniently made on a large scale by aconventional co-extrusion process in which the various film and adhesivelayers are combined within the die head in the molten phase and extrudedthrough a single slit, to yield a multilayer film. In coextrusionprocesses, the adhesives preferably have higher melt viscosities thanadhesives used for compression bonding. The viscosities of thecomponents in a coextrusion process should have comparable meltviscosities (within a factor of a 10).

On a laboratory scale, samples of multilayer films and sheets are madeby compression molding i.e. by heating stacked layers of the films andsheets and the adhesive layers, which are also in film or sheet form,under pressure to a temperature above the melting point of the LCP andadhesive layers. Films and sheets that are to be laminated togethergenerally have a thickness in the range of about 0.01 mm to about 10 mm.

The adhesives identified above are also suitable for use ascompatibilizers in making polymer blends. The blends are made byconventional blending methods, most typically by feeding the polymersand adhesives simultaneously into an extruder and mixing them in themelt phase in the extruder. Twin screw extruders are generally preferredfor making blends.

The practice of the invention is shown by the following examples, whichare illustrative only and should not be viewed as limiting the scope ofthe invention.

EXAMPLES Example 1

Synthesis of LCPs

The LCPs used in evaluating multilayer films were either commerciallyavailable or were made by methods similar to the method shown below formaking a copolymer of about 73 mole % 4-hydroxybenzoic acid (HBA), 27%of 6-hydroxy-2-naphthoic acid (HNA), and 0.2% of 5-sulfoisophthalic acid(SSI).

A pilot scale reactor was charged with 150.4 lbs (493.8 moles) of HBA,75.8 lbs (182.7 moles) of HNA, and 0.8 lbs (1.35 moles) of SSI.Following vacuum deaeration, acetic anhydride (154.3 lbs, 1.0 mole %excess) was charged into the reactor and the water in the cold fingercondenser was turned on as an aid to control reflux. The mixture wasthen stirred at 45 rpm and heated according to the following temperatureprofile:

    __________________________________________________________________________            Stage                                                                         1 2  3  4  5  6  7  8  9  10 11 12                                    __________________________________________________________________________    Final Temp (° C.)                                                              25                                                                              125                                                                              130                                                                              140                                                                              150                                                                              200                                                                              210                                                                              220                                                                              335                                                                              340                                                                              340                                                                              340                                     Time (min.)  1  50  10  40  20  45  5  7 115  10  10 360                    __________________________________________________________________________

After 7 to 8 hours the final temperature of 340° C. was reached. Thewater in the cold finger was turned off when the reaction temperaturereached 300° C. After holding at 340° C. for 30 minutes, the vacuumstripping cycle was started during stage 12, and the stirring rate wasreduced to 25 rpm. Full vacuum (7 mm Hg) was typically reached in 45minutes. The mixture was heated at 340° C. under full vacuum for anadditional period of time to obtain the targeted stirring torque (basetorque+700 in-lbs). After reaching the target torque the vacuum wasbroken by allowing nitrogen back into the reactor. The polymer was heldat 340° C. while it was extruded from the reactor through a 5 hole diewith nitrogen pressure over 35-45 minutes. The polymer strands werecooled in a water trough and then sent through a chopper, and thereactor chip was collected in a drum. Samples for polymer evaluationwere collected at the beginning, middle, and end of the extrusion. Thepolymer was tumble dried, sieved, and weighed. The typical yield was 154pounds (77%).

Example 2

Sample Preparation and Testing

LCP films were prepared by extruding the LCP in the molten phase througha die with vacuum applied at the venting port to remove volatiles. Theextrusion line was a conventional pilot scale extrusion line, producing2-mil thick LCP films. Polypropylene and the adhesives were each madeinto films with dimensions of 16.5 cm×21.5 cm×1-1.5 mm thick bycompression molding on a Wabash Compressor at a temperature about 20° C.above the melting point of the polymer.

For screening purposes, structures having two layers, either of LCP andadhesive or of polypropylene and adhesive, are first made by heating theLCP or polypropylene film on fluoropolymer coated aluminum foil in anoven to a temperature about 20° C. above the melting temperature. Afterthe polymer softens, the adhesive layer is placed on top, and thencovered with a fluoropolymer coated aluminum release sheet and a 2-poundsteel weight. The pressure of the weight is maintained for about 5minutes, and then the heat and pressure are removed. The adhesivebonding of the polypropylene or LCP to the adhesive is measuredqualitatively as follows. The free ends of the two film layers in thetest piece are grasped by hand and pulled apart. The force needed topull them apart is rated qualitatively on a scale of "1" to "4", where"1" means that adhesion is poor, with no force being required toseparate the layers, and "4" means excellent adhesion (the strips cannotbe separated by hand). If the LCP and polypropylene bond well to thesame adhesive (i.e. are rated "3" or "4" using the same adhesive) thenthey are expected to also attach to each other using the same adhesivesto form a multilayer film. The results of the tests are presented inTable 1. Results with adhesives that did not give good adhesion are notincluded in Table 1.

Three layer films were made in some of the cases where it was predictedthat good quality three-layer films can be made, based on the screeningtests described above. Since good three-layer films were obtained inagreement with the predictions resulting from the screening tests, onlya portion of the three layer films that were expected to have goodadhesion were actually made. Three layer films are made by the followingmethod.

A test strip of the LCP (about 2.54 cm×15.24 cm×2 mil) is placed on afluoropolymer coated aluminum release sheet in an oven at a temperatureapproximately 30° C. above the softening point of the LCP. When visualinspection indicates that the polymer has softened (typically 2-3minutes), a 2.54 cm test strip of the candidate adhesive is placed ontop of the softened polymer. A fluoropolymer coated aluminum releasesheet is placed on top of the adhesive and a 2 lb steel weight is set ontop of the release sheet. After approximately 5 minutes the material isremoved from the oven and allowed to cool to room temperature and thealuminum release sheet is removed. The polypropylene layer is thenapplied by placing the LCP/adhesive structure within a 12.7 cm steelframe on top of a fluoropolymer coated aluminum release sheet lying onthe platen of a hot press machine set approximately 20° C. above themelting temperature of the polypropylene. A 2.54 cm strip ofpolypropylene film is placed on top of the adhesive, and fluropolymercoated aluminum release sheet is placed on top of the material. Two tonsof pressure is applied for 10 minutes and then the pressure is released.The material is removed from the platen and allowed to cool to roomtemperature.

Quantitative measurements of the strengths of the bonds between the LCPand polypropylene are carried out using a modified Simple Lap JointTest, as set forth in ASTM test method D 1002-94. The test is reallydesigned for bonded metal specimens, but is suitable for comparativetesting of bonded polymer films. Samples of 4 mm thick multilayer filmsare prepared with 1/2" of overlap for testing. The films are pulledapart using an Instron tensile tester with an angle of peel of 0°. Thesesamples exhibit levels of adhesion between the layers that arecomparable to the adhesion between layers in commercial samples ofmultilayer films (high density polyethylene and ethylene vinyl alcohol)that are used in automobile fuel tanks.

Example 3

Coextrusion of a Multilayer Film

Multilayer films are coextruded using a pilot line designed for makingmultilayer fims. The pilot line has three extruders with screw diameterof 3.5, 2.0 and 1.5 inches. The polymeric material having the greatesttotal thickness in the coextruded film is generally extruded with theextruder having the largest screw diameter. The molten polymer streamsare delivered to the feed block in channels in which the streams aredivided and then combined again so that they emerge from the die lips tomake a multilayer film, which then impinges on a chill roll and isfinally taken up on a roll winder. During the extrusion the overallthickness of the extruded film is continuously monitored by a betagauge. By means of this equipment, several multilayer films are made.One example is the following 5-layer structure:

Polypropylene, 3 mils

Adhesive, 1 mil

LCP, 2 mils

Adhesive, 1 mil

Polypropylene, 3 mils

The LCP is Experimental Polymer 3, which is a copolymer of4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, terephthalic acid,4,4'-biphenol, and resorcinol, as described in U.S. Pat. No. 5,656,714.The polypropylene (Montell Type KY 6100) is a commercial grade suitablefor making fibers and films. The adhesive is MACROMELT Q5353, obtainedfrom Henkel Corporation, Adhesives, Industrial Specialities Division, LaGrange, Ill.

Example 4

Adhesion of Polyolefin Blend to Polypropylene and LCP's

MACROMELT® Q5353 polyolefin blend showed good adhesion to all of theconventional polymers that were tested (HDPE, polypropylene,polycarbonate, poly(ethylene terephthalate), and poly(phenylenesulfide)), achieving a score of 4 with all five polymer films using thequalitative test method for adhesion described above. It also adheredwell to all of the LCP's that were tested, except VECTRA® B resin, whereit still had acceptable adhesion (score of 3) (see Table 1). It is thusthe one adhesive tested that was good for making multilayer films ofpolycarbonate, polyethylene, polypropylene, poly(ethyleneterephthalate), poly(phenylene sulfide), and LCP's in any order orcombination. It is truly surprising that this material could be a"universal adhesive" for multilayer films of conventional polymers andLCP's.

Example 5

Adhesion of Blend of Polypropylene-graft-maleic Anhydride and Dimer AcidBased Polyamide to Polypropylene and LCP's

Neither POLYBOND® 3002 polypropylene-graft-maleic anhydride orMACROMELT® 6239 polyamide adheres well to both LCP's and topolypropylene. However, a 50/50 (wt/wt) blend of the two adhesives bindswell to both materials, achieving a score of 4 using the qualitativetest for polypropylene and for three of the five LCP's tested (VECTRA® Aand L and Experimental Polymer 2). The blend also bonded acceptably(score of 3) to the other two LCP's that were tested. The blend ofadhesives is thus expected to be useful for forming bilayer films ofpolypropylene and LCP's.

Compatibilization Tests

The adhesives for making multilayer films also act as compatibilizersfor making blends of the same polymers that the adhesives bind together.For example, a blend of a fiber grade polypropylene (Montell Type KY6100) with Experimental Polymer 1 was made and evaluated. The blendcontained 10% by weight LCP and 90% by weight polypropylene. Inaddition, an antioxidant (NAUGUARD™ 10 from Ciba-Geigy) and an additivewhich is a compatibilizer for some combinations of polymers but is notan effective compatibilizer for polypropylene and LCP's (NUCREL™ 0903ethylene-methacrylic acid copolymer from DuPont) were included at levelsof 0.2% and 0.5% by weight respectively for all the samples that weretested. The combinations were compounded with compatibilizers disclosedherein by a single or double pass through an extruder. The compoundswere cast into film. The films that included these compatibilizers had abetter, more uniform appearance than the films that did not include thecompatibilizers.

The compounds were also made into films by extrusion, and the tensileproperties were measured by ASTM method D1876. The results for thecontrol (without the compatibilizer) and the two samples with thecompatibilizer follow:

(1) No compatibilizer--tensile modulus, 1.44 GPa; yield stress, 22.5MPa;

(2) 1% by weight of a 50:50 blend of POLYBOND® 3002 and MACROMELT®6239--tensile modulus, 1.69 GPa; yield stress, 29.5 MPa;

(3) 1% by weight of a 40:60 blend of POLYBOND® 3002 and MACROMELT®6239--tensile modulus, 1.85 GPa; yield stress, 29.9 MPa.

Thus, the blends that include the compatibilizers taught herein haveimproved appearance and improved tensile properties compared with blendswithout the compatibilizers. This applies to other combinations thanjust the LCP/polypropylene example above.

It is to be understood that the above-described embodiments of theinvention are illustrative only and that modification throughout mayoccur to one skilled in the art. Accordingly this invention is not to beregarded as limited to the embodiments disclosed herein.

                  TABLE 1                                                         ______________________________________                                        BOND STRENGTH.sup.1 BETWEEN                                                     LCP'S, POLYPROPYLENE, AND ADHESIVES                                                           MACROMELT ®                                                                            BLEND OF                                         LCP Q5353 ADHESIVES.sup.2                                                   ______________________________________                                        VECTRA ® A                                                                              4            4                                                    VECTRA ® B 3 3                                                            VECTRA ® L 4 4                                                            EXPERIMENTAL 4 3                                                              POLYMER 1                                                                     EXPERIMENTAL 4 4                                                              POLYMER 2                                                                     EXPERIMENTAL 4 --                                                             POLYMER 3                                                                     POLYPROPYLENE 4 4                                                           ______________________________________                                         .sup.1 Scale of 1-4; 4 is good, 3 is acceptable, and 1 and 2 are not          acceptable.                                                                   .sup.2 50:50 blend of MACROMELT ® 6239 and POLYBOND ® 3002       

We claim:
 1. A multilayer film comprising a polypropylene layer, athermotropic liquid crystalline polymer layer, and a hot melt adhesivelayer between said layers, wherein said hot melt adhesive is selectedfrom the group consisting of (1) a polyolefin blend comprising asubstantially crystalline first poly(α-olefin), a substantiallyamorphous second poly(α-olefin), and an oligomer of a third α-olefin,which has at least 8 carbon atoms in the α-olefin monomer; and (2) ablend of poly(propylene-graft-maleic anhydride) and a dimer acid basedpolyamide in a ratio of about 30:70 to about 70:30 by weight, andwherein said liquid crystalline polymer layer consists essentially of athermotropic liquid crystalline polymer.
 2. The multilayer film asrecited in claim 1, wherein said hot melt adhesive is a polyolefin blendsold under the name MACROMELT® Q5353.
 3. The multilayer film as recitedin claim 1, wherein said hot melt adhesive is a blend of (a)poly(propylene-graft-maleic anhydride) having a melting point of atleast about 130° C. and a melt flow index rate of at least about 4 g/10min. at 230° C. under a 2.16 kg weight, measured in accordance with ASTMMethod D-1328, and (b) dimer acid-based polyamide having a meltviscosity of about 55 poise to about 85 poise at 225° C., wherein saidpoly(propylene-graft-maleic anyhydride) and said dimer acid basedpolyamide are present in a weight ratio of about 70:30 to about 30:70.4. The multilayer film as recited in claim 1, wherein said hot meltadhesive is a blend of a poly(propylene-graft-maleic anhydride) soldunder the trademark POLYBOND® 3002 and a dimer acid based polyamide soldunder the trademark MACROMELT®
 6239. 5. The multilayer film as recitedin claim 1, wherein said thermotropic liquid crystalline polymer filmcomprises a polymer derived from one or more monomers selected from thegroup consisting of terephthalic acid, isophthalic acid,1,4-hydroquinone, resorcinol, 4-aminobenzoic acid, 4-hydroxybenzoicacid, 4-aminophenol, 1,4-phenylenediamine, 4,4'-biphenol,4,4'-biphenyldicaboxylic acid, 6-hydroxy-2-naphthoic acid,2,6-naphthalenedicaboxylic acid, and 2,6-dihydroxynaphthalene.
 6. Themultilayer film as recited in claim 1, wherein said thermotropic liquidcrystalline polymer film is made from a thermotropic liquid crystallinepolymer selected from the group consisting of (1) a polymer thatconsists essentially of monomer units derived from 4-hydroxybenzoic acidand 6-hydroxy-2-naphthoic acid; (2) a polymer that consists essentiallyof monomer units derived from 6-hydroxy-2-naphthoic acid, terephthalicacid, and 4-aminophenol; (3) a polymer that consists essentially ofmonomer units derived from 4-hydroxybenzoic acid, 6-hydroxy-2-napthoicacid, 4,4'-biphenol, terephthalic acid, and 4-aminophenol; (4) a polymerthat consists essentially of monomer units derived from 4-hydroxybenzoicacid, 6-hydroxy-2-naphthoic acid, hydroquinone, and terephthalic acid;(5) a polymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and5-sulfoisophthalic acid; (6) a polymer that consists essentially ofmonomer units derived from 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoicacid, 4,4'-biphenol, terephthalic acid, and resorcinol; and (7) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 4,4'-biphenol andterephthalic acid.
 7. A multilayer film as recited in claim 1, whereinsaid thermotropic liquid crystalline polymer layer, said polypropylenelayer, and said hot melt adhesive layer each have a thickness in therange of about 0.01 mm to about 10 mm.
 8. A method of laminating athermotropic liquid crystalline polymer film and a polypropylene filmtogether, wherein said thermotropic liquid crystalline polymer film andsaid polypropylene film are heated under a compressive force with a hotmelt adhesive between said thermotropic liquid crystalline polymer filmand said polyethylene film to a temperature above the melting points ofsaid thermotropic liquid crystalline polymer film, said polypropylenefilm, and said hot melt adhesive for a time sufficient to melt said hotmelt adhesive and bind said polypropylene film and said thermotropicliquid crystalline polymer film to one another to yield a laminatedfilm, wherein said hot melt adhesive is selected from the groupconsisting of (1) a polyolefin blend comprising a substantiallycrystalline first poly(α-olefin), a substantially amorphous secondpoly(α-olefin), and an oligomer of a third α-olefin, which has at least8 carbon atoms in the α-olefin monomer; and (2) a blend ofpoly(propylene-graft-maleic anhydride) and a dimer acid based polyamidein a ratio of about 30:70 to about 70:30 by weight, and wherein saidthermotropic liquid crystalline polymer film consists essentially of athermotropic liquid crystalline polymer.
 9. The method as recited inclaim 8, wherein said hot melt adhesive is in the form of a film. 10.The method as recited in claim 8, wherein said thermotropic liquidcrystalline polymer film and said polypropylene film each have athickness in the range of about 0.01 mm to about 10 mm.
 11. The methodas recited in claim 8, wherein said hot melt adhesive is selected fromthe group consisting of: (1) a polyolefin blend; and (2) a blend ofpoly(propylene-graft-maleic anhydride) and a dimer acid based polyamide.12. The method as recited in claim 8, wherein said hot melt adhesive isselected from the group consisting of: (1) a polyolefin blend comprisingisotactic polypropylene, a substantially amorphous secondpoly(α-olefin), and an oligomer of a third α-olefin, which has at least8 carbon atoms in the α-olefin monomer; and (2) a blend of (a)poly(propylene-graft-maleic anhydride) having a melting point of atleast about 1 30° C. and a melt flow index rate of at least about 4 g/10min. at 230° C. under a 2.16 kg weight, measured in accordance with ASTMMethod D-1328, and (b) a dimer acid-based polyamide having a meltviscosity of about 55 poise to about 85 poise at 225° C., wherein saidpoly(propylene-graft-maleic anyhydride) and said dimer acid basedpolyamide are included in a weight ratio of about 70:30 to about 30:70.13. The method as recited in claim 8, wherein said polyolefin blend is ahot melt adhesive sold under the trademark MACROMELT®
 05353. 14. Themethod as recited in claim 8, wherein said hot melt adhesive is a blendof a poly(propylene-graft-maleic anhydride) sold under the trademarkPOLYBOND® 3002 and a dimer acid based polyamide sold under the trademarkMACROMELT®
 6239. 15. The method as recited in claim 8, wherein saidthermotropic liquid crystalline polymer film comprises a polymer derivedfrom one or more monomers selected from the group consisting ofterephthalic acid, isophthalic acid, 1,4-hydroquinone, resorcinol,4-aminobenzoic acid, 4-hydroxybenzoic acid, 4-aminophenol,1,4-phenylenediamine, 4,4'-biphenol, 4,4'-biphenyldicarboxylic acid,6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid, and2,6-dihydroxynaphthalene.
 16. The method as recited in claim 8, whereinsaid thermotropic liquid crystalline polymer film is made from athermotropic liquid crystalline polymer selected from the groupconsisting of (1) a polymer that consists essentially of monomer unitsderived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; (2) apolymer that consists essentially of monomer units derived from6-hydroxy-2-naphthoic acid, terephthalic acid, and 4-aminophenol; (3) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-napthoic acid, 4,4'-biphenol,terephthalic acid, and 4-aminophenol; (4) a polymer that consistsessentially of monomer units derived from 4-hydroxybenzoic acid,6-hydroxy-2-naphthoic acid, hydroquinone, and terephthalic acid; (5) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and5-sulfoisophthalic acid; (6) a polymer that consists essentially ofmonomer units derived from 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoicacid, 4,4'-biphenol, terephthalic acid, and resorcinol; and (7) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, terephthalic acid,and 4,4'-biphenol.
 17. A method of making a multilayer film thatcomprises a polypropylene layer and a thermotropic liquid crystallinepolymer layer bound to one another, wherein said thermotropic liquidcrystalline polymer, said polypropylene, and a hot melt adhesive arecombined in the molten state in a die head and extruded through a slitto yield a multilayer film, wherein said hot melt adhesive is selectedfrom the group consisting of (1) a polyolefin blend comprising asubstantially crystalline first poly(α-olefin), a substantiallyamorphous second poly(α-olefin), and an oligomer of a third α-olefin,which has at least 8 carbon atoms in the α-olefin monomer: and (2) ablend of poly(propylene-graft-maleic anhydride) and a dimer acid basedpolyamide in a ratio of about 30:70 to about 70:30 by weight.
 18. Themethod as recited in claim 17, wherein said hot melt adhesive isselected from the group consisting of: (1) a polyolefin blend comprisingisotactic polypropylene, a substantially amorphous secondpoly(α-olefin), and an oligomer of a third α-olefin, which has at least8 carbon atoms in the α-olefin monomer; and (2) a blend of (a)poly(propylene-graft-maleic anhydride) having a melting point of atleast about 130° C. and a melt flow index rate of at least about 4 g/10min. at 230° C. under a 2.16 kg weight, measured in accordance with ASTMMethod D-1328, and (b) a dimer acid-based polyamide having a meltviscosity of about 55 poise to about 85 poise at 225° C., wherein saidpoly(propylene-graft-maleic anyhydride) and said dimer acid basedpolyamide are included in a weight ratio of about 70:30 to about 30:70.19. The method as recited in claim 17, wherein said polyolefin blend isa hot melt adhesive sold under the trademark MACROMELT® Q5353.
 20. Themethod as recited in claim 17, wherein said hot melt adhesive is a blendof a poly(propylene-graft-maleic anhydride) sold under the trademarkPOLYBOND® 3002 and a dimer acid based polyamide sold under the trademarkMACROMELT®
 6239. 21. The method as recited in claim 17, wherein saidthermotropic liquid crystalline polymer film comprises a polymer derivedfrom one or more monomers selected from the group consisting ofterephthalic acid, isophthalic acid, 1,4-hydroquinone, resorcinol,4-aminobenzoic acid, 4-hydroxybenzoic acid, 4-aminophenol,1,4-phenylenediamine, 4,4'-biphenol, 4,4'-biphenyldicarboxylic acid,6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid, and2,6-dihydroxynaphthalene.
 22. The method as recited in claim 17, whereinsaid thermotropic liquid crystalline polymer film is made from athermotropic liquid crystalline polymer selected from the groupconsisting of (1) a polymer that consists essentially of monomer unitsderived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; (2) apolymer that consists essentially of monomer units derived from6-hydroxy-2-naphthoic acid, terephthalic acid, and 4-aminophenol; (3) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-napthoic acid, 4,4'-biphenol,terephthalic acid, and 4-aminophenol; (4) a polymer that consistsessentially of monomer units derived from 4-hydroxybenzoic acid,6-hydroxy-2-naphthoic acid, hydroquinone, and terephthalic acid; (5) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and5-sulfoisophthalic acid; (6) a polymer that consists essentially ofmonomer units derived from 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoicacid, 4,4'-biphenol, terephthalic acid, and resorcinol; and (7) apolymer that consists essentially of monomer units derived from4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, terephthalic acid,and 4,4'-biphenol.